882 PECTIN. 



is insoluble in alcohol, soluble in water, the solution is neutral 

 to test paper, insipid or tasteless ; it is not adhesive like gum 

 arabic. The dried pectin swells up in water, and more readily 

 in cold than in hot water ; with one hundred times its weight of 

 water it forms a jelly, with a larger quantity only a gelatinous 

 liquid. It resembles vegetable mucilage in many of its pro- 

 perties ; with nitric acid it first forms saccharic acid, afterwards 

 mucic acid. It is dissolved by an excess of alkali, and converted 

 into the following isomeric acid. 



Pectic acid. This substance is conveniently obtained by 

 grating yellow carrots to a pulp,, expressing the juice, washing 

 the marc several times successively with distilled or rain-water, 

 and expressing it well again. The marc is then diffused through 

 six times its weight of pure water, free from earthy salts, and 

 solution of pure caustic potash gradually added by small por- 

 tions. The mixture is then heated and made to boil for about 

 a quarter of an hour, and the boiling liquor filtered through 

 a cloth. The mixture is known to have boiled long enough, 

 when a small portion of it, after being filtered, is found to 

 become a jelly on adding to it a drop or two of acid. 



The pectic acid may be separated by a strong acid, but 

 as it is then difficult to wash, it is preferable to precipitate it by 

 chloride of calcium, which gives the pectate of lime, in the form 

 of a coagulated jelly completely insoluble in water. This jelly 

 is washed on a cloth, boiled with water, to which a little hydro- 

 chloric acid is added, which dissolves the lime and leaves the 

 pectic acid ; the last is then washed with cold water. Pectic 

 acid remains as a transparent and colourless jelly, faintly acid, 

 very slightly soluble in cold water, but more soluble in boiling 

 water. The filtered solution does not become solid on cooling, 

 but it coagulates and forms a jelly when alcohol is added to it, 

 or sugar, which has the property of dissolving pectic acid, and 

 transforming it after some time into a jelly, a property on which 

 is founded the preparation of the jelly of currants, apples, goose- 

 berries, &c. ; fruits of which the juice mixed with sugar coagulates 

 in the course of a few days. When evaporated to dryness, 

 pectic acid resembles pectin in appearance, and has the same 

 composition. It is a bibasic acid. The pectates possess the 

 property of forming a jelly when precipitated, in common with 

 the acid. Those only containing an alkaline base are soluble in 



